<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .box {
            width: 1000px;
            margin: 30px auto 0;
            border: 1px solid black;
            display: flex;  
        }

        .box .column {    
            width: calc(100% / 3 - (10px + 10px + 20px) * 2);
            height: 100px;
            border: 10px solid red;
            padding: 0 10px;
            margin: 0 20px;
        }
    </style>
</head>
<body>
    <div class="box">
        <div class="column"></div>
        <div class="column"></div>
        <div class="column"></div>
    </div>
</body>
</html>